Roof bits are used in a violent environment in which heavy loads and torques are continually applied to the roof bits at a high rate. One inch diameter roof bits are commonly operated at about 250-600 rpm and 1000-8000 pounds thrust. These conditions also generate excessive heat at the tip end of the roof bit assembly.
A hard wear resistant insert for use in a center vacuum rotary drill bit is typically formed of cemented tungsten carbide and is secured by brazing the insert within a slot formed within a top working surface of the body of the rotary drill bit. The hard wear resistant insert secured within the top working surface of the rotary drill bit body typically wears or dulls before the drill bit body becomes worn and unusable such that the user of the center vacuum rotary drill bit must either replace the entire rotary drill bit, attempt to replace the insert with a new insert of similar size, or attempt to resharpen the insert. Replacement of the entire center vacuum rotary drill bit is costly and resharpening of the insert may only be performed a limited number of times before the top working surface of the drill bit body frictionally engages the material to be cut.
In U.S. Pat. Nos. 5,310,015; 5,184,925 and 5,226,489, to Woods et al., a roof bit assembly is disclosed wherein a support bar is positioned between the insert bit and bit body for adjusting the height that the insert bit extends beyond the top surface of the roof bit body. In U.S. Pat. No. 5,184,925, the insert body has a semicircular notch 50 therein and the support bar has a corresponding convex portion for cooperating with the depression. The support bar in these roof bits results in additional assembly time during original manufacturing or when replacing inserts onto a bit body. The assembly of these roof bits can be even more time consuming and cumbersome in the field. The support bar also requires maintaining additional parts and undesirable expanding inventories.
In U.S. Pat. No. 4,356,873, to Dziak, an insert is provided with a notch that cooperates with a projection 38 on a retainer clip that must be fixed into a slot of the bit body. The retainer clip is laterally held in position in the bit body slot by flanges 40 that cooperate with the exterior cylindrical wall of the bit body.
There is a need in the industry for a mining roof bit that requires a minimum number of parts, is easy to assemble accurately, braze, and comparatively inexpensive in cost. There is also a need in the industry for an insert that is securely held in the bit body during drilling operations and is not as readily knocked loose from the bit body.